1. Field of the Invention
The invention relates to a mobile radio terminal comprising a speech processor.
2. Discussion of the Related Art
In the field of speech processing, speech signals to be processed often contain noise signal components, which leads to a degradation of the speech quality and thus specifically to a deteriorated understandability. This problem occurs, for example, in mobile radio terminals which are used in private cars and have a hands-free facility. Speech signals received from microphones of the hands-free facility which are installed in the private car contain, on the one hand, speech signal components generated by the user (speech source) of the mobile radio terminal inside the private car, and, on the other hand, noise signal components which consist of other ambient noise and, during a ride, in essence, of engine and driving noise.
"IEEE Transactions on Acoustics, Speech, and Signal Processing, Vol. ASSP-29, No. 3, June 1981, pp. 582-587" has disclosed an arrangement for adaptively estimating time delays of two strongly correlated signals in digital systems. Either signal is delayed by a controllable delay element. The delay values of the delay element are adaptively matched with the correlated signals. Calculating the delay values is effected via an algorithm which has meanwhile been referenced an LMS algorithm (Least Mean Square) by those skilled in the art. This algorithm is based on the minimization of the power i.e. of the squared error values which are obtained from the difference between the delayed and the undelayed signal. The core of the LSM algorithm is the recursive calculation of the delay values via estimates for the gradients of the power of the error values.
To find the error values in the state of the art cited above, the difference between two sample values of two oppositely time-shifted signals is formed while one of the signals is delayed. The appropriate delay value is rounded to an integer multiple of a sampling interval of the signals. During this rounding operation, convergence problems occur because considerable variations of the rounded delay values occur when very small error values are reached. During one sampling interval the delay values then vary between two rounded delay values.